Booya (also spelled Booyah) is a term used to express happiness or joy after something beneficial happens to you. It has relevance in the RBI world because of a long-running thread on the forums. It was originally posted by Pitoface on the Anything Goes Board on September 2nd, 2004 and continues to get bumped to this day. You'll see countless references to Booyah throughout the forums
The original contents of the BOOYA! thread was a video of a sexual act called dogs in the bathtub. It was incredibly raunchy and perverse, making it immediately appealing to the assorted malcontents that frequent the forum. The video, sadly, is no longer available, but thread that spawned is an instant classic and considered a "must read" for new forum members. Even without the original video, the BOOYA! thread is chock full of perverse pictures and hilarious commentary.